P0848

Transmission Fluid Pressure Sensor/Switch B Circuit High

P0848 is a generic OBD-II powertrain diagnostic trouble code: Transmission Fluid Pressure Sensor/Switch B Circuit High. It is logged by the engine control unit when the trans monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0848
Group
Powertrain
System
Trans
Severity
Warning (MIL on, possible limp mode)
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What P0848 means

P0848 — Transmission Fluid Pressure Sensor/Switch "B" Circuit High — is stored when the PCM or TCM measures a voltage on the sensor B signal line that exceeds the manufacturer's maximum allowable threshold. The most common electrical cause is a short to the reference voltage supply (typically 5 V), which holds the signal line at or near its maximum value regardless of actual hydraulic pressure. A broken signal wire between the sensor and TCM can also produce a high reading if the input pin floats toward the pull-up voltage inside the module.

With the sensor pinned at maximum voltage, the TCM interprets this as extremely high transmission line pressure. Depending on the control strategy, it may reduce commanded pressure aggressively — leading to slipping clutches and missed shifts — or it may flag the implausibility and enter fail-safe mode. Either outcome accelerates clutch wear if the vehicle continues to be driven.

Diagnosis follows the opposite logic from P0847: rather than looking for opens or shorts to ground, the technician must trace the signal circuit for a short to the 5 V reference wire, a chafed harness where the signal conductor contacts a voltage source, or a sensor whose internal element has failed high. Mechanical causes (excessively high actual line pressure) are uncommon but possible on vehicles with a stuck pressure regulator valve.

Common causes

Most-frequently reported root causes when P0848 is logged.

  • 1
    Short circuit between the sensor B signal wire and the 5 V reference supply wire (harness chafe or pinched conduit).
  • 2
    Failed transmission fluid pressure sensor B with internal element shorted to the reference voltage side.
  • 3
    Open signal wire between the sensor and TCM causing the module's internal pull-up to hold the input high.
  • 4
    Damaged wiring harness connector with a bent terminal bridging the signal and reference pins.
  • 5
    Faulty electronic pressure control solenoid causing abnormally high actual line pressure that pins the sensor output.
  • 6
    Stuck-closed pressure regulator valve in the valve body generating excessively high hydraulic pressure.
  • 7
    Contaminated transmission fluid causing valve body restriction and elevated line pressure.
  • 8
    PCM/TCM internal fault incorrectly reading or processing the sensor signal circuit.

Symptoms drivers notice

Check engine or transmission warning light illuminated.
Slipping or soft gear engagement as the TCM reduces commanded line pressure in response to a falsely high pressure signal.
Delayed or missed upshifts and downshifts.
Transmission entering limp (fail-safe) mode with limited gear availability.
Transmission overheating from clutch slippage caused by under-commanded line pressure.
Torque converter clutch hunting or failing to lock up at cruising speed.

How to diagnose P0848

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool, read all stored codes and freeze-frame, and confirm the signal voltage is above the high threshold in live data.
  2. 2
    Inspect the sensor wiring harness for chafing where the signal wire could contact the 5 V reference wire or another voltage source.
  3. 3
    With the sensor connector unplugged, measure the voltage on the signal pin at the harness side — any voltage above 0 V indicates a short to a power source.
  4. 4
    Check wiring continuity from the signal pin at the connector to the TCM input — an open in this wire can cause the module's pull-up to float high.
  5. 5
    Substitute a known-good transmission fluid pressure sensor B; if signal voltage drops to normal range, the original sensor failed internally.
  6. 6
    If sensor and wiring pass, perform a mechanical line pressure test with a calibrated gauge to check for a legitimately stuck pressure regulator valve.
  7. 7
    If actual line pressure is within specification but the code persists with a new sensor, suspect a TCM fault and perform manufacturer-prescribed module diagnostics.

Related powertrain codes

Frequently asked questions

What is the difference between P0848 and P0847?

P0848 means the sensor circuit voltage is above the maximum threshold — typically from a short to the 5 V reference or a floating open input. P0847 means the voltage is below the minimum threshold — typically from a short to ground or an open signal wire pulling the sensor output down.

Can P0848 cause clutch slippage?

Yes. If the TCM reads a falsely high pressure signal, it may reduce commanded line pressure to compensate, leaving clutch packs under-applied. This causes slipping, especially under load, and accelerates clutch wear if driving continues.

Is an open signal wire a cause of P0848?

Yes, on many TCM designs. An open in the signal wire between the sensor and TCM causes the module's internal pull-up resistor to hold the input pin near the reference voltage, which can trigger the circuit-high threshold — the opposite of what many technicians expect.

Can high actual line pressure cause P0848?

It is possible if a stuck pressure regulator valve drives line pressure to an extreme level that pins the sensor output at its voltage ceiling. However, this is an uncommon mechanical cause — electrical faults (short to reference, open signal wire, failed sensor) account for the majority of P0848 cases.

Disabling P0848 in software

RaceTune can permanently disable P0848 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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